Compression Test Results/Question - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 11-22-2005, 02:33 PM   #1
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Default Compression Test Results/Question

Cyl 2,3,4,5 = 180ish

Cyl 6 = 170ish

Cyl 1...

This is strange, the first time you attach the gauge, turn the engine over, the highest reading you get is about 165ish. If you immediately release the pressure in the meter, and crank the engine again, you get like just about 180.

I duplicated this a couple times, and I don't think it'* how long my wife was turning the car over. The other cylinders went to 180 without fuss.
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Old 11-22-2005, 02:39 PM   #2
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how are you performing the test? I was leaving plugs etc in and that is the wrong way.

Paging Don...can you please remind us how to do this test properly....Don to the thread....Paging Don...
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Old 11-22-2005, 02:41 PM   #3
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thanks Billboost for your help

I followed the procedure in the GM 97 Service Manual...

Took all the plugs out, in other words. I disabled the fuel and ignition systems... the only thing I didn't do, was yank out the PCM-- to scared of breaking it!

Is that OK?
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Old 11-22-2005, 02:42 PM   #4
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Have you done a wet and dry test?
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Old 11-22-2005, 02:44 PM   #5
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Dry only

it was my understanding a wet test was only necessary if a cylinder was below 90psi, or not within 10% of the others.

I thought that 165ish for Cylinder 1 initially was not quite out of the 10% range...
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Old 11-22-2005, 02:48 PM   #6
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That compression is pretty good... Nothing to worry about there...

Usually it takes a few strokes to get a good reading

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Old 11-22-2005, 03:17 PM   #7
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In general, the way i was taught and way ive done it is, Unhook plug from ICM, remove all plugs, hook a battery charger up to the batter to keep constant steady power. let it crank over 6 times, since its a V6, on that last crank record the reading.
My shop teacher last year, a journeyman since 1970, showed us, I trust his knowledge hehe.
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